Non-digital inks and printing elements suitable for Magnetic Ink Character Recognition (MICR) printing are generally known. The two most commonly known technologies are ribbon-based thermal printing systems and offset technology. For example, U.S. Pat. No. 4,463,034 discloses heat sensitive magnetic transfer element for printing MICR, comprising a heat resistant foundation and a heat sensitive imaging layer. The imaging layer is made of ferromagnetic substance dispersed in a wax and is transferred on a receiving paper in the form of magnetic image by a thermal printer which uses a ribbon. U.S. Pat. No. 5,866,637 discloses formulations and ribbons which employ wax, binder resin and organic molecule based magnets which are to be employed for use with a thermal printer which employs a ribbon. MICR ink suitable for offset printing using a numbering box are typically thick, highly concentrated pastes consisting for example in about over 60% magnetic metal oxides dispersed in a base containing soy-based varnishes. Such inks are, for example, commercially available at Heath Custom Press (Auburn, Wash.). Digital water-based ink-jet inks composition for MICR applications using a metal oxide based ferromagnetic particles of a particle size of less than 500 microns are disclosed in U.S. Pat. No. 6,767,396. Water-based inks are commercially available from Diversified Nano Corporation (San Diego, Calif.).
The present embodiments relate to solvent-based ink compositions. These ink compositions can be used for ink jet printing in a variety of applications. In addition to providing desirable ink qualities, the present embodiments are directed to magnetic inks for use in specific applications. The ink of the present embodiments comprise magnetic nanoparticles that are coated with various materials to prevent the exposure of the nanoparticles to oxygen. The present embodiments are also directed to a solvent-based magnetic ink that provides robust prints.
The present embodiments are directed to solvent-based magnetic inks which comprise an organic solvent, an optional dispersant, an optional synergist, an optional antioxidant, an optional viscosity controlling agent, an optional colorant, and coated magnetic nanoparticles comprising a magnetic core and a coated shell disposed thereover. These magnetic inks are required for specific applications such as Magnetic Ink Character Recognition (MICR) for automated check processing and security printing for document authentication. One of the challenges in formulating such a solvent-based ink, however, is that many of these metal nanoparticles are pyrophoric and extremely sensitive to air and water. For example, iron nanoparticles can burst into flame instantly upon exposure to air. As such, uncoated magnetic metal nanoparticles are a serious fire hazard. As such, large scale production of the solvent-based inks comprising such particles is difficult because air and water need to be completely removed when handling the particles. In addition, the ink preparation process is particularly challenging with magnetic pigments because inorganic magnetic particles are incompatible with organic base components. Lastly, a problem associated with the use of the magnetic solid inks is the solid ink vehicle is designed for normal office use and not the highly abrasive environment of multiple passes through a magnetic reader. As a result, a magnetic solid ink print may wear off quickly during machine-reading process, either for MICR or for document authentication procedures.
Thus, there is a need for a magnetic ink which can be printed with piezoelectric print-heads and which can be made both safely and provides robust prints compatible with solvent-based compositions.
Thus, while the disclosed solid ink formulation provides some advantages over the prior formulations, there is still a need to achieve a formulation that not only provides the desirable properties of a solvent-based ink but is also more easily produced and derived from components that do not require special handling conditions.